20250626 09:30 Chapter 6 : Understanding Data Types Better

                              

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Integers – The Short, the Long, and the Compiler

How big can an int be?

• 16-bit system (Turbo C):
  int = -32,768 to +32,767

• 32-bit system (VC++):
  int = -2,147,483,648 to +2,147,483,647

Top bit = sign

• 1 = Negative 

• 0 = Positive 

Old 16-bit code may not work on new systems (like Itanium ).

Long and Short

• Want more space? Use long. Want to save space? Use short.

• Usual sizes:

  • short → 2 bytes

  • long → 4 bytes

• Syntax:
  short int a; or just short a;
long int b; or just long b;

• Want to force a constant to be long? Use L like a boss:
  23L (Not to be confused with 23 liters of Coke)

Signed & Unsigned – Mood Settings for Variables

Only Positive Vibes? Use unsigned!

By default, int can be positive or negative.
But if you only want positives (like for counting people):

unsigned int num;

Doubles the positive range
No minus signs = no wasted space!

Also works with:

• unsigned short

• unsigned long

Chars – Small but Tricky

• Normally, char stores ASCII values (like 'A' = 65)

• But char can also be signed or unsigned:

  • signed char = -128 to +127

  • unsigned char = 0 to 255

• Beware: Storing big numbers like char ch = 291; causes weird behavior.
  Why? Because char overflows and wraps around. So 291 turns into 35 – like magic, but evil.

Infinite Loop Example:

char ch;

for (ch = 0; ch <= 255; ch++)

  printf("%d %c", ch, ch);

Looks fine? But surprise! It's an infinite loop. Why?
Because char can't go beyond 127. After that, it jumps to -128. Round and round it goes like a washing machine.

Fix it: Use int ch; or do this trick:

unsigned char ch;
for (ch = 0; ch <= 254; ch++)
  printf("%d %c", ch, ch);
printf("%d %c", ch, ch);

Floats, Doubles & Long Doubles – Surfing Real Numbers

• float – 4 bytes, good enough for daily math

• double – 8 bytes, more accurate

• long double – 10 bytes, for super nerdy numbers like black hole physics 

Declaration:

float x;
double y;
long double z;

Format Specifiers (very important!):

• %f – float

• %lf – double

• %Lf – long double

Data Type Cheatsheet:

Type	Range	Bytes	Format
signed char	-128 to +127	1	%c
unsigned char	0 to 255	1	%c
short signed int	-32768 to +32767	2	%d
short unsigned int	0 to 65535	2	%u
signed int	-32768 to +32767	2	%d
unsigned int	0 to 65535	2	%u
long signed int	-2147483648 to +2147483647	4	%ld
long unsigned int	0 to 4294967295	4	%lu
float	-3.4e38 to +3.4e38	4	%f
double	-1.7e308 to +1.7e308	8	%lf
long double	-1.7e4932 to +1.7e4932	10	%Lf